The present invention relates to the use of hemoglobin derivatives for determining plasma and/or blood volume as well as preparations for determining plasma and/or blood volume, which contain a hemoglobin derivative with carbon monoxide as ligand.
We describe as blood volume the entire quantity of blood circulating, which is composed of plasma volume and erythrocyte volume. An adequate blood flow through the organs is necessary for the maintenance of all organ functions. Losses of blood and fluid lead to an uneven distribution of blood volume for the maintenance of vital functions. In such cases, it may come about that there is a reduced blood flow through some organs and damage to these as a consequence. The volume of plasma as a measure for the state of the filling of the cardio-vascular system and for determining an adequate blood flow in patients with blood or fluid loss is thus of great significance for clinical daily practice and for research.
In the prior art therefore a number of processes have been developed with which plasma and/or blood volume can be determined.
Standard processes for determining the volume of erythrocytes and of plasma volume by the use of radio-active labelling had already been proposed in 1973 by the International Society for Hematology (British Journal of Hematology, Vol. 25 (1973), 801-814). For determining volume of erythrocytes, a process was recommended wherein the erythrocytes of a patient are mixed with a solution that contains 51Cr, the mixture is incubated for 15 minutes and finally the erythrocytes are obtained and washed. The radioactive labelled erythrocytes are injected again into the patient. 10 and 20 minutes after the injection, blood samples of 5 to 10 ml are taken from the patient, in which the erythrocytes are lysed and the volume can be determined by means of the radioactivity measured.
In the corresponding process for determining plasma volume, human serum albumin labelled with radioactive iodine is given to the patient""s plasma. The taking of samples and assessment ensues in essence as with the process for determining erythrocyte volume.
In view of the radiation loading, routine injection, especially repeated input of radioactively marked isotopes, is completely excluded in clinical daily practice. Correspondingly, these standard procedures are only used for scientific purposes or with special disease patterns, as for example polycythemia true.
Furthermore, in the prior art processes were developed for determining plasma volume, where dye compounds were introduced into the blood of patients as analytes. Here, for example, Evans Blue or Indocyanin green (ICG) are injected intravenously and the concentration of dye is determined spectrometrically or densitometrically after mixing with the blood plasma and taking of a sample (Haller et al, Anaesthetist, Vol. 41 (1992), 115-120; and Gehring et al., Infusion therapy and Transfusion medicine, Vol. 23 (1996), 86-91). It is possible to ascertain the plasma volume from the dilution of the dye by the plasma. However, it has emerged that these processes involve some risks to the patients. The dye Evans Blue is under suspicion of possessing mutagenic properties and thus is unsuitable for determining plasma volume in humans. The introduction of ICG should ensue centre-venously or centre-arterially and the samples should be taken arterially. It is therefore necessary to apply centre-venous and/or arterial catheters in order to perform the measurement. The application or insertion of the catheters is not without dangers to the patients and very costly. What is more, ICG which is bound with the plasma protein, interferes with pulsoximetry, a clinically routinely applied non-invasive process for the determining of oxygen saturation (Scheller et al., Anesthesiology, Vol. 65 (1986), 550-552) and merely possesses a plasma half value time of 3.2 min. The dye is eliminated exclusively by the liver (Haller et al, in the stated place). With plasma protein losses, for example, extravasation of albumin following burns, too high plasma volumes are found when determining plasma volume because of the binding of ICG to plasma proteins.
Although determining the plasma volume with ICG has already been known in the prior art for over 30 years (Bradley, E. C. and Barr J. W., Life Sci., Vol. 7 (1968), 1001-1007), it was not possible to implement this process in clinical daily practice, because of the problems mentioned.
The determining of the volume of erythrocytes by labelling with the dye fluorescein has already been carried out in the prior art (Ohrt et al., Ansth. Analog., Vol. 87 (1998), 1234-1238). This is used to label the erythrocytes of a patient with fluorescein and re-inject these into the patient. After mixing with the blood, samples are taken and an analysis is made for the content of fluorescein by flow cytometry. Because of the fact that the marking of erythrocytes and the subsequent analyses lasts more than an hour, the applicability of this process is limited to those problem areas where an acute determination of the volume situation is of low relevance.
Finally, there have been developed processes for determining blood volume in which a defined quantity of carbon monoxide is given to the patient into breath-ventilation and finally the carbon monoxide saturation of the blood is determined (Christensen et al., Anaesthesiol. Scand., Vol. 730, (1993), 622-627; and Poulsen et al., Eur. J. Appl. Physiol., Vol. 77 (1998), 457-461). The application of a defined carbon monoxide quantity is very costly and limited to patients who are ventilated artificially.
According to a further embodiment of this process, blood is taken from patients and treated with carbon monoxide. The erythrocytes which contain hemoglobin bound with carbon monoxide, are reinjected and the concentration of carbon monoxide in the blood is determined after thorough mixing and sample taking (Obata et al., British Journal of Anaesthesia, Vol. 81 (1998), 940-944). This process reduces however the capacity of the blood to transport oxygen, as a part of the blood of the patients is prevented from absorbing the oxygen because of the bound carbon monoxide. These processes can therefore not be applied to patients with low oxygen reserves.
In view of the problems described in the prior art regarding processes for immediate determining of plasma and/or blood volume these are not routinely applied in clinical daily practice. The condition of the volume of the patients today is thus ascertained as before indirectly through measuring the hemodynamic circulation parameters such as blood pressure, heart pulse, pulmonary pressures and heart pace volumes. These measurements, however, do not allow any statement about the total and peripheral blood and plasma volumes.
It is therefore the problem underlying the present invention to make available a method which can be used for determining the blood and plasma volume in clinical daily practice.
This problem is solved in accordance with the invention by use of hemoglobin derivatives for determining plasma and blood volume. The hemoglobin derivatives are stable chromoproteins with a molecular weight of at least 64 kDa.
In the context of the present invention, it could be shown surprisingly, that these hemoglobin derivatives are particularly suited for determining plasma volume, as the hemoglobin derivatives and/or ligands bound with these are meaureable in low concentrations. This means that application of hemoglobin is possible in a quantity which does not bring about an alteration in the volume or a change in other parameters of the blood.
Further, the present invention concerns the use of hemoglobin derivatives in a diagnostic process for determining plasma and/or blood volume, wherein a defined quantity of corresponding hemoglobin derivative is given to a patient and the mixture of hemoglobin derivatives with the patient""s blood is awaited, at least one sample is taken from the patient, the content in hemoglobin derivative or the content in hemoglobin-derivative bound ligands in the sample is determined, and the plasma and/or blood volume ascertained.
The dilution of the applied hemoglobin derivative can thus either ensue through determining the hemoglobin concentration in the blood or plasma and/or through determining the concentration of the hemoglobin derivative bound ligands.